At a court hearing, Justice Department attorney Michael Dreeben said Rosenstein discussed specific legs of the investigation with Mueller months before he wrote a classified memo in August that outlined Mueller's directive.

Dreeben argued that the Justice Department shouldn't have to produce documentation of those early talks about the investigation's scope that occurred before Rosenstein's August 2 memo. Rosenstein has been overseeing Mueller's investigation following the recusal of Attorney General Jeff Sessions, according to CNN.

While Rosenstein and Mueller's communication about the Russia probe may help the special counsel's office defend its criminal case against former Trump campaign chairman Paul Manafort, Mueller's team is also indirectly pushing back against the President and Republicans' assertions that the investigation is rogue and corrupt.

"We have an alive and awake acting attorney general who's looking at this investigation, [and] knows what's going on," Dreeben said.

Read alsoMueller was authorized to investigate Paul Manafort's work for Ukraine – mediaManafort has alleged in court that Mueller's office overstepped its authority by charging him with crimes related to his work before the 2016 campaign. His attorney also demanded they see records of Rosenstein and Mueller's discussions before August.

Mueller's appointment unfolded in May with a public notice from Rosenstein, directing the special counsel to investigate links between the Russian government and the campaign and other matters that arose from the investigation. The August memo, which was unveiled earlier this month and gets into more specifics, was "reflective of decisions that had already been made," Dreeben said.

Rosenstein's August 2 memo gives Mueller the green light to investigate Manafort for his lobbying work in Ukraine, years before the campaign. It also outlines several other still-undisclosed allegations that Mueller could investigate and says Mueller could look into allegations that Manafort colluded with Russians during the campaign. Manafort has pleaded not guilty to the foreign lobbying and financial charges. He has not been charged with crimes related to Russian collusion.

Read alsoEx-FBI chief says Russians may have "kompromat" on TrumpJudge Amy Berman Jackson of the US District Court for the District of Columbia, says it's unlikely the Justice Department fully knew what Mueller should pursue when he was first appointed.

Investigators shouldn't have to "start with the conclusion" that crimes were committed, she added. Instead, prosecutors could follow the question of whether Manafort had links to Russians. That work, even if it didn't connect directly to Manafort's time on the campaign, would be essential to any criminal investigation, she said, and Dreeben later echoed her.